The specific aims of the proposed study are to determine if external heat applied to the calves can prevent the high incidence of venous thrombosis occurring in patients with acute myocardial infarction and to determine if the administration of digitalis to patients with myocardial infarction affects venous flow velocity and the peripheral circulation. Venous thrombosis will be objectively determined by the use of I125 labelled fibrinogen in patients with acute myocardial infarction. One lower limb will be treated with moist heat while the opposite limb will serve as the control. In the second part of the study, arterial blood flow and venous volume-pressure curves will be measured by venous occlusion plethysmography. Central venous pulmonary arterial and wedge pressures will be followed with a Swan Ganz catheter and cardiac outputs measured by the thermodilution technique. These variables will be studied before and after acute treatment with a rapidly acting digitalis preparation. Data will thus be obtained on changes in the peripheral and central circulations that occur with acute myocardial infarction and on the effect of digitalization on these changes.